1. Field of the Invention
The present invention relates to a quaternary ammonium salt which may be used for a photo-curable antifogging composition. More particularly, the present invention relates to a quaternary ammonium salt which may be used for the photo-curable antifogging composition which may be applied to the surface of substrates such as glass, various plastic materials and the like to provide antifogging properties on the surface of these substrates, a preparation method for the ammonium salt and the photo-curable antifogging composition including the same.
2. Description of the Prior Art
When articles such as swimming goggles, lenses, coverlets of measuring instruments, window glasses, various films and the like are placed in an environment in which a temperature difference between the internal and the external side is large, tiny water droplets are formed on the surface of these articles. In order to overcome this predicament, a method of applying an antifogging agent to a surface of an article has been suggested. Also, various research for a photo-curable antifogging composition that may be cured by UV irradiation has been conducted.
A conventional antifogging composition comprising hydrophilic substances such as polyvinylalcohol crosslinked with a catalyst such as peroxide is disclosed in U.S. Pat. No. 5,262,475. However, the processing temperature of the composition is about 150.degree. C. Thus, it is difficult to apply the composition to a thin film due to the high processing temperature. Moreover, the crosslinked antifogging layer becomes sticky and then flows upon contact with water. The surface hardness of the layer is merely 6B as Pencil Hardness. Therefore, the layer may be scratched readily and thus cannot be used for a long time.
Another conventional antifogging method is to apply a solution of a surface active agent to a surface of a substrate. However, the substrate treated by such a method provides only a temporary antifogging property. An conventional antifogging method is to apply a polymeric surface active agent to a surface of the substrate in order to impart long-lasting antifogging property thereto.
Still another conventional method wherein a polymeric surface active agent is incorporated into a coating composition is also disclosed in Korean Patent Publication No. 95-14730. According to this method, however, a thermal drying process which should be continued for 20 to 180 seconds is needed to remove residual polar solvent from the antifogging composition. Moreover, UV irradiation which lasts for 20 to 60 seconds is required to cure the composition. Consequently, this method has a drawback of a low productivity caused by a two-step curing precess and a long treating time. Moreover, the antifogging property of the substrate treated by this method also reduces suddenly after 1 to 2 months.
To overcome the above described predicaments of the prior arts, the inventors of the present invention carried out extensive studies, and as a result found that antifogging compositions comprising a specific quaternary ammonium salt which contains photo-curable functional groups, and a photo-curable oligomer, provide good surface hardness, excellent adhesion properties, and excellent antifogging properties lasting a long time.